v6ops Working Group E. Levy-Abegnoli
Internet-Draft G. Van de Velde
Intended status: Informational C. Popoviciu
Expires: March 6, 2011 Cisco Systems
J. Mohacsi
NIIF/Hungarnet
September 02, 2010
IPv6 Router Advertisement Guard
<draft-ietf-v6ops-ra-guard-07.txt>
Abstract
When using IPv6 within a single L2 network segment it is possible and
sometimes desirable to enable layer 2 devices to drop rogue RAs
before they reach end-nodes. In order to distinguish valid from
rogue RAs, the L2 devices can use a spectrum of criteria, from a
static scheme that blocks RAs received on un-trusted ports, or from
un-trusted sources, to a more dynamic scheme that uses Secure
Neighbor Discovery (SEND) to challenge RA sources.
This document reviews various techniques applicable on the L2 devices
to reduce the threat of rogue RAs.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 6, 2011.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Model and Applicability . . . . . . . . . . . . . . . . . . . 4
3. Stateless RA-Guard . . . . . . . . . . . . . . . . . . . . . . 6
4. Stateful RA-Guard . . . . . . . . . . . . . . . . . . . . . . 6
4.1. State Machine . . . . . . . . . . . . . . . . . . . . . . 7
4.2. SEND-based RA-Guard . . . . . . . . . . . . . . . . . . . 8
5. RA-Guard Use Considerations . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
When operating IPv6 in a shared L2 network segment without complete
SEND support by all devices connected or without the availability of
the infrastructure necessary to support Secure Neighbor Discovery
(SEND) [RFC3971], there is always the risk of facing operational
problems due to rogue Router Advertisements generated maliciously or
unintentionally by unauthorized or improperly configured routers
connecting to the segment.
There are several examples of work done on this topic which resulted
in several related studies [reference1] [reference2]
[reference3].This document describes a solution framework for the
rogue-RA problem where network segments are designed around a single
or a set of L2-switching devices capable of identifying invalid RAs
and blocking them. The solutions developed within this framework can
span the spectrum from basic (where the port of the L2 device is
statically instructed to forward or not to forward RAs received from
the connected device) to advanced (where a criteria is used by the L2
device to dynamically validate or invalidate a received RA, this
criteria can even be based on SEND mechanisms).
2. Model and Applicability
RA-Guard applies to an environment where all messages between IPv6
end-devices traverse the controlled L2 networking devices. It does
not apply to a shared media such as an Ethernet hub, when devices can
communicate directly without going through an RA-Guard capable L2
networking device.
Figure 1 illustrates a deployment scenario for RA-Guard.
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Block Allow
+------+ incoming +---------+ incoming +--------+
|Host | RA | L2 | RA | Router |
| |----------------| device |--------------| |
+------+ +----+----+ +--------+
|
|Block
|incoming
|RA
|
|
|
+---+---+
| Host |
| |
+-------+
Figure 1
RA-Guard does not intend to provide a substitute for SEND based
solutions. It actually intends to provide complementary solutions in
those environments where SEND might not be suitable or fully
supported by all devices involved. It may take time until SEND is
ubiquitous in IPv6 networks and some of its large scale deployment
aspects are sorted out such as provisioning hosts with trust anchors.
It is also reasonable to expect that some devices might not consider
implementing SEND at all such as IPv6 enabled sensors. An RA-Guard
implementation which SEND-validates RAs on behalf of hosts would
potentially simplify some of these challenges.
RA-Guard can be seen as a superset of SEND with regard to router
authorization. Its purpose is to filter Router Advertisements based
on a set of criteria, from a simplistic "RA disallowed on a given
interface" to "RA allowed from pre-defined sources" and up to full
fledge SEND "RA allowed from authorized sources only".
In addition to this granularity on the criteria for filtering out
Router Advertisements, RA-Guard introduces the concept of router
authorization proxy. Instead of each node on the link analyzing RAs
and making an individual decision, a legitimate node-in-the-middle
performs the analysis on behalf of all other nodes on the link. The
analysis itself is not different from what each node would do: if
SEND is enabled, the RA is checked against X.509 certificates
[RFC4861]. If any other criteria is in use, such as known L3
(addresses) or L2 (link-layer address, port number) legitimate
sources of RAs, the node-in-the middle can use this criteria and
filter out any RA that does not comply. If this node-in-the-middle
is a L2 device, it will not change the content of the validated RA,
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and avoid any of the ND-proxy pitfalls.
RA-Guard intends to provide simple solutions to the rogue-RA problem
in contexts where simplicity is required while leveraging SEND in an
context environment consisting of with a mix of SEND capable devices
(L2 switches and routers) and devices that do not consistently use
SEND. Furthermore, RA-Guard is useful to simplify SEND deployments,
as only the L2 switch and the routers are required to carry
certificates (their own and the trust anchor certificates).
3. Stateless RA-Guard
Stateless RA-Guard examines incoming RAs and decide whether to
forward or block them based solely on information found in the
message or in the L2-device configuration. Typical information
available in the frames received, useful for RA validation is:
o Link-layer address of the sender
o Port on which the frame was received
o IP source address
o Prefix list
The following configuration information created on the L2-device can
be made available to RA-Guard, to validate against the information
found in the received RA frame:
o Allowed/Disallowed link-layer address of RA-sender
o Allowed/Disallowed ports for receiving RAs
o Allowed/Disallowed IP source addresses of RA-sender
o Allowed Prefix list and Prefix ranges
o Router Priority
Once the L2 device has validated the content of the RA frame against
the configuration, it forwards the RA to destination, whether unicast
or multicast. Otherwise, the RA is dropped.
An example of a very simple stateless RA-Guard implementation could
be a small L2-switch for which there is one interface "statically-
configured" as the interface connecting to a router, while all other
interfaces are for non-router devices. With his small static setup
the only interface forwarding RAs will be the pre-assigned router
interface, while the non-router interfaces block all RAs.
4. Stateful RA-Guard
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4.1. State Machine
Stateful RA-Guard learns dynamically about legitimate RA senders, and
store this information for allowing subsequent RAs. A simple
stateful scheme would be for the L2-device to listen to RAs during a
certain manual determined period of time, where the start of the
listening-period and the duration of the listening-period for a
single instance is controled by the manual intervention. As result
the L2-device can then allow subsequent RAs only on those ports on
which valid RAs were received during this period. Often the LEARNING
state will only be activated by manual configuration when a new IPv6
router is provisioned on the L2-network.
A more sophisticated stateful scheme is based on SEND, and is
described in Section 4.2.
The state machine for stateful RA-Guard can be global, per-interface,
or per-peer, depending on the scheme used for authorizing RAs.
When RA-Guard is SEND-based, the state machine is per-peer and
defined in [RFC3971].
When RA-Guard is using a discovery method, the state-machine of the
RA-Guard capability consists of four different states:
o State 1: OFF
A device or interface in RA-Guard "OFF" state, operates as if
the RA-Guard capability is not available.
o State 2: LEARNING
A device or interface in the RA-Guard "Learning" state is
actively acquiring information about the IPv6 routing devices
connected. The learning process takes place over a pre-defined
unique period in time, set by manual configuration or it can be
event triggered. The information gathered is compared against
pre-defined criteria; criteria similar as the stateless RA-
Guard rules to qualify the validity of the RAs.
In this state, the RA-Guard enabled device or interface is
either blocking "all" RAs until their validity is verified or,
alternatively it can temporarily forward "all" the RAs until
their validity is verified.
Once the L2-device has identified through "Learning" the valid
IPv6 routers and hence also identified the valid RAs, it
transtions each interface from "LEARNING" into either BLOCKING
state if there was no valid IPv6 router discovered at the
interface, or transitions the interface into FORWARDING state
if there was a valid IPv6 router discovered.
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o State 3: BLOCKING
A device or interface running RA-Guard and in Blocking state
will block ingress RA-messages.
An interface can transition from BLOCKING state into FORWARDING
state directly if explicitly instructed by the L2-device
operator.
An interface can transition from BLOCKING state into LEARNING
state if either explicitly told by the L2-device operator or by
a triggered event.
o State 4: FORWARDING
A device or interface running RA-Guard and in Forwarding state
will accept valid ingress RAs and forward them to their
destination.
An interface can transition from FORWARDING state into BLOCKING
state directly if explicitly instructed by the L2-device
operator.
An interface can transition from FORWARDING state into LEARNING
state if either explicitly told by the L2-device operator or by
a triggered event.
The transition between these states can be triggered by manual
configuration or by meeting a pre-defined criteria.
4.2. SEND-based RA-Guard
In this scenario, the L2 device is blocking or forwarding RAs based
on SEND considerations. Upon capturing an RA on the interface, the
L2-device will first verify the Cryptographically Generated Addresses
(CGA) [RFC3971] address and the RSA (Rivest, Shamir and Adleman
algorithm for public-key cryptography) signature, as specified in
section 5 of [RFC3971]. RA should be dropped in case of failure of
this verification. It will then apply host behavior as described in
section 6.4.6 of [RFC3971]. In particular, the L2 device will
attempt to retrieve a valid certificate from its cache for the public
key referred to in the RA. If such certificate is found, the L2
device will forward the RA to destination. If not, the L2 device
will generate a Certification Path Solicitation (CPS) [RFC3971],
sourced with UNSPECIFIED address, to query the router certificate(s).
It will then capture the Certification Path Advertisements (CPA)
[RFC3971], and attempt to validate the certificate chain. Failure to
validate the chain will result in dropping the RA. Upon validation
success, the L2 device will forward the RA to destination and and
store the router certificate in its cache.
In order to operate in this scenario, the L2-device should be
provisioned with a trust anchor certificate, as specified in section
6 of [RFC3971]. It may also establish a layer-3 connectivity with a
Certificate Revocation List (CRL) Certification Path Advertisement
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server and/or with and NTP server. Bootstrapping issue in this case
can be resolved by using the configuration method to specify a
trusted port to a first router, and SEND-based RA-Guard method on all
other ports. The first router can then be used for Network Time
Protocol (NTP) [RFC5905] and CRL connectivity.
5. RA-Guard Use Considerations
The RA-Guard mechanism is effective only when all messages between
IPv6 devices in the target environment traverse controlled L2
networking devices. In the case of environments such as Ethernet
hubs, devices can communicate directly without going through an RA-
Guard capable L2 networking device, the RA-Guard feature cannot
protect against rogue-RAs.
RA-Guard mechanisms do not offer protection in environments where
IPv6 traffic is tunneled.
6. IANA Considerations
There are no extra IANA consideration for this document.
7. Security Considerations
Once RA-Guard has setup the proper criteria, for example, it
identified that a port is allowed to receive RAs, or it identified
legitimate sources of RA, or certificate base [RFC4861], then there
is no possible instances of accidently filtered legitimate Router
advertisements assuming the RA-Guard filter enforcement follows
strictly the RA-Guard set criteria.
in Section 4.1 a simple mechanism to learn dynamical the valid IPv6
routers connected to a L2-device is explained. It is important that
this LEARN state is only entered intentionally by manual
configuration. The list of learned IPv6 routers should be verified
by the network manager to make sure that it corresponds with the
expected valid RA list. This procedure will make sure that either
accidently or intentionally rogue RAs are blocked by RA-guard.
8. Acknowledgements
The authors dedicate this document to the memory of Jun-ichiro Hagino
(itojun) for his contributions to the development and deployment of
IPv6.
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9. References
9.1. Normative References
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4158] Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.
Nicholas, "Internet X.509 Public Key Infrastructure:
Certification Path Building", RFC 4158, September 2005.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
9.2. Informative References
[reference1]
LORIA/INRIA, "NDPMon - IPv6 Neighbor Discovery Protocol
Monitor (http://ndpmon.sourceforge.net/)", November 2007.
[reference2]
KAME Project, "rafixd - developed at KAME - An active
rogue RA nullifier (http://www.kame.net/dev/cvsweb2.cgi/
kame/kame/kame/rafixd/)", November 2007.
[reference3]
Hagino (itojun), Jun-ichiro., "Discussion of the various
solutions (http://ipv6samurais.com/ipv6samurais/
demystified/rogue-RA.html)", 2007.
[reference4]
Chown, Tim. and Stig. Venaas, "Rogue IPv6 Router
Advertisement Problem (draft-ietf-v6ops-rogue-ra-00.txt)",
May 2009.
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Authors' Addresses
Eric Levy Abegnoli
Cisco Systems
Village d'Entreprises Green Side - 400, Avenue Roumanille
Biot - Sophia Antipolis, PROVENCE-ALPES-COTE D'AZUR 06410
France
Phone: +33 49 723 2620
Email: elevyabe@cisco.com
Gunter Van de Velde
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 2704 5473
Email: gunter@cisco.com
Ciprian Popoviciu
Cisco Systems
7025-6 Kit Creek Road
Research Triangle Park, North Carolina NC 27709-4987
USA
Phone: +1 919 392-3723
Email: cpopovic@cisco.com
Janos Mohacsi
NIIF/Hungarnet
18-22 Victor Hugo
Budapest H-1132
Hungary
Phone: tbc
Email: mohacsi@niif.hu
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